1. Field of the Invention
The present invention relates to a method for manufacturing an optical waveguide by a direct writing method and the optical waveguide manufactured by using the same, and more particularly, to a method of improving a refractive index profile of the optical waveguide by overlapping two or more beams using a Gaussian laser. Also, the present invention provides a method for manufacturing the optical waveguide which is capable of improving waveguide characteristics such as offset structure of a S-bend type optical waveguide and an asymmetrical curved optical waveguide by individually adjusting each of the overlapped laser beams, independently.
2. Description of the Prior Art
The method for manufacturing the optical waveguide using the laser direct writing method has the procedure of focusing the laser beam on a photo-sensitive polymer in order to pass through a writing process and increasing the refractive index of the written pattern to form the optical waveguide.
Up to now, an optical device and an optical component has been developed based on semiconductor material and inorganic silica system material for the purpose of implementing high speed of an optical communication, mass communication. But, recently, polymer material is the concerned about more and more, because it has merits such as a low cost and a simple process.
Various methods for manufacturing the optical waveguide have been used using the polymer material, and, in general, there are a photolithography method, a hot embossing method, a direct ultraviolet patterning method, and a laser direct writing method.
The photolithography method includes very complicate processes such as a step of coating a cladding material on a substrate, a step of baking, a step of coating a core material, a step of applying a photoresist, a step of exposing using a photomask, a step of developing and a step of etching.
In the hot embossing method, a core portion structure is molded in under clad material using a mold master, core material is inserted into the molded structure, an over clad is covered thereon, and ultraviolet rays are irradiated in order to cure the core material and adhere the over clad thereto.
In the ultraviolet direct patterning method, after a under clad is formed on a plane substrate, ultraviolet cured polymer is coated thereon as a core layer. And, after exposed to the ultraviolet ray by using the photomask, a core pattern is formed by using a polymer developer and then upper clad material is coated.
The laser direct writing method is based on a laser micro-machining technique. FIG. 1 is a concept diagram illustrating a general laser direct writing method. The light from the laser passes through a tunable neutral density filter and a shutter and is irradiated on the substrate through the objective lens of a microscope. On the substrate, the clad material is coated and then the core layer is coated. By simple process of focusing the laser beam on the core layer and writing a desired pattern, the optical waveguide can be manufactured. The refractive index of the pattern written by the laser becomes larger than that of the adjacent area, which is not written, and, the optical waveguide, therefore, is formed through total reflection principle.
The laser direct writing method has advantages in shortening of the process time, low cost and the application to large area, because of the simple process without the photomask.
However, in case the optical waveguide is implemented through the laser direct writing method according to prior art, it is difficult to implement a sharpness in boundary (between core material and clad material) of the optical waveguide, because of the nature of the light. The laser beam in the laser writing process has Gaussian distribution, the step profile of the core in the optical waveguide is not clearly formed. As a method for improving the step-like index profile of the optical waveguide, there is the laser direct writing method using a donut-shaped beam (TEM01 mode). As a method for generating the donut-shaped beam, a diffracting phase mask or a hologram (CGH: Computer Generated Hologram) has been used.
Since the laser irradiates a light beam with a Gaussian distribution, the step profile of the optical waveguide is not clearly formed. It is why an additional bending loss in the curved region of the optical waveguide is caused.